A sheet mainly composed of ultra fine fiber and elastomer has an excellent characteristic not exhibited by natural leather, and has been used for clothing, chair upholstery and automobile interior materials more widely year by year. Recently, a sheet excellent in stretchability has been demanded particularly from the viewpoint of comfortability to wear in clothing use and moldability in material use. Various studies have been made for such demand.
For example, a method for inserting woven or knitted material using polytrimethylene terephthalate fiber into textile for artificial leather as described above is described in Patent Document 1. Although this method utilizes stretchability due to the crystal structure of polytrimethylene terephthalate, the stretchability is low because of high-density nonwoven fabric with single fibers entangled with each other and allowed polyurethane to constrain the woven or knitted material from moving firmly. In addition, the fiber length of an ultra fine fiber for forming the nonwoven fabric is as short as 20 mm or less that repetitive stretching untangles the entanglement to bring deterioration in grade.
Also, a method for inserting woven or knitted material using potential crimping fiber composed of high shrinkage polyester and low shrinkage polyester is described in Patent Document 2. This method imparts stretchability, in which the woven or knitted material composed of potential crimping fiber is heat-treated to develop crimp, and the crimp is integrated with a fiber capable of converting into ultra fine fibers by needle punching. In the woven or knitted material made of the fiber having developed crimp, the crimped fiber is so easily hooked on a needle as to be cut when integrated with a fiber capable of converting into ultra fine fibers. Thus, the woven or knitted material with the cut fiber develops stretchability with difficulty. Polyurethane is provided after developing crimp in the woven or knitted material, and so the form of the sheet itself is fixed and stretchability thereof is developed with difficulty.
In addition, a method for inserting woven or knitted material using polyurethane fiber into nonwoven fabric for artificial leather is described in Patent Document 3. However, it is known that polyurethane is deteriorated with time, and the fabric by the method vanishes in stretchability due to use for many years. As in Patent Document 1, the fiber length of an ultra fine fiber is so short that repetitive stretching untangles the entanglement in the ultra fine fibers themselves to bring deterioration in grade.
That is to say, a method for obtaining a sheet excellent in surface appearances, touch, stretch ratio and stretch-back ratio has not been obtained so far.
Patent Document 1: Japanese Unexamined Patent Publication No. 11-269751
Patent Document 2: Japanese Unexamined Patent Publication No. 2000-336581
Patent Document 3: Japanese Unexamined Patent Publication No. 2004-91999